RE: [PATCH v2 10/10] vfio/pci: Add VFIO_DEVICE_GET_PCI_HOT_RESET_GROUP_INFO

From: "Liu, Yi L" <yi.l.liu@intel.com>
To: Alex Williamson <alex.williamson@redhat.com>,
	"Tian, Kevin" <kevin.tian@intel.com>
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Subject: RE: [PATCH v2 10/10] vfio/pci: Add VFIO_DEVICE_GET_PCI_HOT_RESET_GROUP_INFO
Date: Tue, 28 Mar 2023 14:38:12 +0000	[thread overview]
Message-ID: <DS0PR11MB7529B6782565BE8489D922F9C3889@DS0PR11MB7529.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20230328082536.5400da67.alex.williamson@redhat.com>

> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Tuesday, March 28, 2023 10:26 PM
> 
> On Tue, 28 Mar 2023 06:19:06 +0000
> "Tian, Kevin" <kevin.tian@intel.com> wrote:
> 
> > > From: Liu, Yi L <yi.l.liu@intel.com>
> > > Sent: Tuesday, March 28, 2023 11:32 AM
> > >
> > > > From: Alex Williamson <alex.williamson@redhat.com>
> > > > Sent: Tuesday, March 28, 2023 3:26 AM
> > > >
> > > > Additionally, VFIO_DEVICE_GET_PCI_HOT_RESET_INFO has a flags arg
> that
> > > > isn't used, why do we need a new ioctl vs defining
> > > > VFIO_PCI_HOT_RESET_FLAG_IOMMUFD_DEV_ID.
> > >
> > > Sure. I can follow this suggestion. BTW. I have a doubt here. This new
> flag
> > > is set by user. What if in the future kernel has new extensions and needs
> > > to report something new to the user and add new flags to tell user? Such
> > > flag is set by kernel. Then the flags field may have two kinds of flags
> (some
> > > set by user while some set by kernel). Will it mess up the flags space?
> > >
> >
> > flags in a GET_INFO ioctl is for output.
> >
> > if user needs to use flags as input to select different type of info then it
> should
> > be split into multiple GET_INFO cmds.
> 
> I don't know that that's actually a rule, however we don't currently
> test flags is zero for input, so in this case I think we are stuck with
> it only being for output.
> 
> Alternatively, should VFIO_DEVICE_GET_PCI_HOT_RESET_INFO
> automatically
> return the dev_id variant of the output and set a flag to indicate this
> is the case when called on a device fd opened as a cdev?  Thanks,

Personally I prefer that user asks for dev_id info explicitly. The major reason
that we return dev_id is that the group/bdf info is not enough for the device
fd passing case. But if qemu opens device by itself, the group/bdf info is still
enough. So a device opened as a cdev doesn't mean it should return dev_id,
it depends on if user has the bdf knowledge.

Regards,
Yi Liu